From changes in local RAAS to structural remodeling of the left atrium: A beautiful cycle in atrial fibrillation

In earlier studies, we reported structural remodeling was associated with atrial fibrillation (AF) and showed that the renin-angiotensin-aldosterone system (RAAS) was linked to AF. It is reasonable to hypothesize that there is a cycle, from RAAS to structural remodeling to AF.

Our study group consisted of 80 patients scheduled for mitral valve replacement surgery. Tissue samples of the left atrial appendages were obtained. Masson's trichrome staining and immunohistochemical staining were performed to assess the extent of fibrosis. Radioimmunoassay was carried out to investigate the expression levels of local RAAS. RAAS-related genes were analyzed by RT-PCR.

There was a significantly increased degree of fibrosis in AF patients compared with sinus rhythm (SR) patients (p = 0.023). There were significant differences in the expression levels of local angiotensin (Ang) II between the SR and the AF groups (p = 0.002). The expression levels of local Ang II correlated with the duration of AF (r = 0.727851, p = 0.001) and with collagen type I (r = 0.672189, p = 0.032). In the AF group, the mRNA expressions of the AT1R and ACE genes were markedly up-regulated in comparison with the SR group (p = 0.021 and p = 0.037).

On the basis of this study, and in combination with results of our previous studies, we demonstrate for the first time that there is a cycle involving RAAS, structural remodeling, and AF. RAAS, structural remodeling, and AF are the principal aspects in this cycle.